How to split a pane vertically in tmux

Splitting a pane vertically in tmux gives one window a left-and-right layout, which is useful when you need to watch two commands at the same time without leaving the current session, such as an editor beside a log view or a shell beside a long-running build.

In tmux's own command names, the default C-b % binding runs split-window -h, which tmux calls a horizontal split because the panes are arranged side by side. This guide keeps the page's vertical-split wording because most readers identify the layout by the vertical divider drawn between the panes.

The new pane opens on the right and becomes active immediately unless -d is used with split-window -h. If the current pane is already too narrow, tmux will refuse the split, and if you changed the prefix or rebound % in ~/.tmux.conf you should use your custom binding or run the command from the tmux command prompt instead.

1. Show pane numbers if the target pane is not obvious.

   C-b q

   The temporary overlay marks each pane and lets one number key jump focus to that pane before you split it.

2. Press the default left-and-right split binding in the active pane.

   C-b %

   If tmux reports there is no space for another pane, enlarge the terminal or close an unused pane before splitting again.

3. List the panes to confirm the window now has a left pane and a right active pane.

   $ tmux list-panes -F '#{pane_index}:#{pane_active}:#{pane_left}:#{pane_right}'
   0:0:0:39
   1:1:41:79

   The fields are pane:active:left:right, so 1:1:41:79 confirms pane 1 is active on the right side; the exact coordinates change with the window width.

4. Move focus back to the left pane when work should continue there.

   C-b Left

   The command-prompt form C-b :split-window -h -d creates the new pane on the right without moving focus into it.

• The page title uses vertical split in the reader sense, but tmux names the left-and-right layout a horizontal split and creates it with split-window -h.
• Use split-window -h -b from the tmux command prompt when the new pane should open on the left instead of the right.
• Use split-window -h -l 80 or split-window -h -l 50% when the new pane needs a fixed width or a percentage of the current window instead of an even split.